The Promise
by Ylhatesprwns
Summary: Everything was done for that sole promise made to her since fifteen years ago... MephiShura. Slight AU-ish.


**Hi all! It's been a long time since I've written any fanfics (mainly due to laziness and lack of motivation). I've recently got into the Ao no Exorcist fandom and found out that I really like the pairing MephistoxShura. It has become one of my new OTPs ;_; The fandom for this pairing is really small and it's totally not enough to satisfying my shipping needs. So ta-da. I've decide to write a fic to contribute to the fandom. *rants***

**Anyway this fic contains some plots that are created by me so it may not stick that closely to the original series. And some very wild guesses at the plot that probably will never happen in the manga. (Sorry. Just couldn't help it).**

Disclaimer: I do not own any of the characters in AnE if not MephiShura would have been canon already.

* * *

_(15 years ago)_

"Shirou-sensei!" A young Shura called out to her teacher, "I've finished training! Can I go eat now?!"

"Of course you can, Shura." The older man nodded his head as he smiled approvingly. Shura ran towards Shirou but stopped when she saw an unfamiliar face behind him. The unknown man was wearing a white coat with a white top hat to match. The dark purple hair that peeked out from under the hat and the polka-dotted bright pink cravat were the only things that contrasted against the white background.

"Shirou-sensei, who's that behind you?" Shura asked cautiously as her hand shifted to her wooden sword.

"Don't worry, Shura. This is my friend, Mephisto Pheles." Shura relaxed after hearing that.

"When did you have such a beautiful daughter, Shirou?"

"She's my student, not my daughter. And don't get any weird ideas. She's still young." Shirou warned.

"I'm not that old, Shirou! I'm only a few years after two hundred!" Mephisto whined. He turned his attention towards the girl who was still standing a few feet away from them. He squatted down and stretched out his hand. "Come over here, Shura-chan was it? Don't worry, I won't harm you even though I'm a demon."

Shura was unsure of how to respond to the friendly new guy. He's a demon. Shura was taught that demons were evil creatures and should not be trusted. She looked at Shirou for approval but he was too busy shrugging and sighing to notice her stares.

"_It's okay Shura, he looks like a nice guy." _

There was an inner turmoil for a few seconds but finally, her feelings won over what was taught to her. Convinced, she walked towards Mephisto as she too, held out her hand to welcome him.

* * *

Shirou's nightmare had come true. It has been years since Shura first met Mephisto. Shura has just turned fifteen recently and has blossomed into a beautiful girl. Her great sword skill has also earned her a place at the exorcist Academy. It was also the age where hormones struck her. Ever since Mephisto has increased his frequency of visits, young Shura had grown to be quite attached to the demon. They would often play tag or have a swordfight during their free time and sometimes Mephisto would tell Shura stories from his "home town". So it wasn't surprising when the fondness became infatuation. Yes. That was what Shirou was worried about. The way Shura's eyes would shine whenever Mephisto dropped by. The way Shura would blush when he teased or touched her. Even the way she laughed when he joked.

An ominous premonition, Shirou thought. It's about time he stepped in.

Shirou walked gravely towards the unknowing couple who were sitting in the garden, laughing merrily.

"Mephisto-san. T-There is something that I would like to tell you." Shura words made Shirou froze in his spot.

"_Am I too late?" _Shirou thought. After thinking through, he decided to stick to the option of hiding behind the sliding door and eavesdropping on their conversation.

"You know you can tell me anything, Shura-chan." Mephisto winked as a small blush crept onto Shura's cheeks.

"A-Actually, I was thinking, would it be p-possible for you to stay by my side f-forever?" After a few stammering and stuttering, the confession was out. Shirou slapped his hand against his forehead.

"_Reject her, Mephisto. Reject!" _Shirou prayed.

"Of course! Anything for you, Shura-chan. Who wouldn't want to stay by a beautiful girl's side forever?" His hands reached over to play with Shura's red strands of hair.

Double slap.

"Promise me you'll stay by my side forever?"

"I, Mephisto Pheles, promised to stay by Shura Kirigakure's side for the rest of his life. Is that good enough?"

Shura let out a delightful chuckle as she hugged the demon.

That night, Shirou confronted Mephisto.

"Do you know what you have gotten yourself into, Mephisto?" Shirou growled. "She's not your toy. Do not play around with her feelings!"

"I'm not, Shirou. I'm a man of my words. Even if I'm a demon, a gentle-demon doesn't go around breaking promises." Mephisto replied in a serious tone.

"With the current situation, do you really think you can keep your promise? Remember our mission? How would you be able to find the time? How would she feel if she knows of our mission?"

"Don't worry. I'll find some way to solve the problem."

"It's not that easy, Mephisto. It's not that easy. You're a demon, she's a human. Humans are more fragile than you think. If you hurt her just once, especially during such delicate time, be prepared to be hated for the rest of your life."

"I'll go find a way, Shirou. I'll start finding now. Just help me convince her that I'll be back."

With that, Mephisto disappeared without a trace, leaving both Shura and Shirou alone.

"Shirou-sensei, where's Mephisto-san?" Shura would ask him.

"He'll be back after running some errands, Shura." And Shirou would reply.

"_Idiot demon, you better hurry up." _Shirou would curse.

This goes on until Shirou's death which was a huge blow to Shura. But even then, Mephisto did not appear. There was no one to console her except herself. In an empty room, she cried for three days, waiting for the demon to visit her, to tell her that everything is going to be okay with him by her side. It was a painful time for her. After three days there was still no news of Mephisto. That was when she finally decided to stop believing in Shirou's and Mephisto's words.

"_Never trust a demon. Never fall in love with a demon." _Shura told herself as she steeled her heart, stashing all her memories with Mephisto at the back of her mind, never to be retrieved…

* * *

_(Present day)_

Their time was almost up. In another few months, the spell binding Gehenna's gate would soon weaken before all hell break loose. Shura was on the edge today. Once again, Mephisto had sent them on another dangerous mission that almost cost them their lives if it wasn't for Okumura Rin. She knew Mephisto was training Rin but this is just too much. It's not like forcing them into dangerous situations will allow them to gain enough power to defeat Satan. She stormed into his office, her heart full of rage and at the same time, apprehension at the impending danger.

"Mephisto Pheles!" The door slammed open as the demon in his chair jumped slightly, startled by the sudden outburst.

"What is it, my dear Shura?" Mephisto managed a greeting.

"I'm sick of all your antics, you demon! You have always been tricking us, using us as your pawns! Do you really want us to die that much?!" Shura flared, "and your secret mission, why don't you ever tell me anything?!"

"I don't like sharing information, Shura, especially not information that can be used against me." The demon replied nonchalantly as his gaze shifted to the ground, like a child trying to hide his mistakes.

"Don't you trust us at all?"

"I trust you, Shura. But you don't trust me."

"Oh tell me about it." Shura mocked sarcastically. "How do I trust someone who refused to tell me anything at all?"

There was a pregnant silent. Shura gave a satisfying smirk when she saw the defeated look on Mephisto's face. His mouth slightly agape, ready to argue against her but no voice had come out yet. It was not long before he regained his composure, eyes hardening in resolution as his gaze went back to Shura's.

"I'm afraid I still can't tell you." Shura gave a loud sigh which was shortly interrupted by the demon. "… but, trust me on this. My plans will not endanger your life…"

There was a pause in the air as Shura held her breath, waiting for him to continue.

"… In fact, I wouldn't want you to die." He broke off eye contact almost immediately the statement came out and went back to looking at the floor. That statement came out more like a mumble instead of a proper sentence but Shura caught it nevertheless.

A light blush tinted her cheeks. She could feel her resolve weakening. In fact, she wasn't even sure why she was blushing. It's not like she was that love-struck fifteen-year-old teenager. Of course Mephisto would want her alive. He needs her for his plans. So why is his statement having such an effect on her?

"It would be a pity to lose such a beautiful woman like you," Mephisto gave her a toothy grin.

"_See? He's just using you again, Shura. Using his sweet words and tricking people into becoming his pawns." _Her mind nagged at her even though her heart was telling her otherwise. That lingering hope that Mephisto really cared for her… maybe it was the way he said it. Or maybe it was that look on his face a few minutes ago… that vulnerable look which was there for that split second.

"So in the end I'm just merely your pawn. Nothing has changed from this talk, Mephisto." That, was her mind speaking. "Since I see no point in continuing this conversation, I shall bid you farewell."

There it was, she is walking out now. It was probably just her after all. Demons are just demons… they do not harbor any trace of feelings. A certain memory was threatening to surface but was violently forced back by Shura. Her chest was hurting.

She stopped walking when Mephisto decided to call out her name once more.

"Shura, watch over Okumura Rin."

"_Is that all he has to say?"_

"I know I know. I'll look after your secret weapon for you."

"And… don't die."

"Stop cursing me, Mephisto. I might really die at this rate." Shura scolded. Actually, that was more than enough to ignite that lingering feeling in her heart. "You know, Mephisto…"

"Hn?"

"Ever since the day I've met you, you really sucked at convincing people." She walked out of her office. She did not dare to turn her head to see what reaction the demon had. Truth is, she did not want to know. She did not want to see that confused look on the demon that would prove her hypothesis on the incapability of demons to feel. She had enough of those feelings.

But alas, what she had missed was a thoughtful look on Mephisto's face…

* * *

_(One year into the future)_

The gruesome fight was over, finally. Rin, together with the help of his friends, has defeated Satan. At the same time, the organization itself has gained lots of damages including the loss of many fine warriors. Mephisto was tired. Very tired. He was involved in the war itself. Fighting against creatures of the same type was never easy even though he is ranked the highest among them. But he had to. In order to let Rin slay Satan, he needs to clear a path, get rid of the creatures from Gehenna. And now, he's sitting on the ground, leaning against the remaining of a pillar that has already collapsed. His breathing was shallow and body worn out. His white coat was stained with blood and mud.

He opened his eyes slowly upon hearing footsteps approaching him. It was Shura's.

"Good to see you alive, Shura." He greeted. His words came out more like a whisper.

"So you've destroyed the organization, you've destroyed Satan. You'll be able to rule over both sides. Are you finally satisfied?" Shura said bitterly. Her bright red hair messed up from the fight and dirt covered her face and body.

"As I've said, my goal was to bring peace to both sides. The destruction of both the organization and Satan was needed for peace to prevail. It will eventually come. I couldn't tell you for fear that you may get yourself into danger. And because of my second mission, I had to speed things up before it's too late. Shirou was right after all, I can't possibly handle two missions without sacrificing my time."

"Second mission?" her voice now carries a hint of curiosity.

"Remember the promise that I've made? I had been thinking really hard on how to fulfill that promise."

"It's not hard, Mephisto."

"Death is a scary thing, Shura. I can be by your side forever but sooner or later you'll be the first to expire. And when you die, what am I to do? I don't think I can bear staring at your old sunken face, watching you leave." Mephisto sighed. "That gave me a new mission. I need to find it… A way to turn you into a demon, or me into a human, so that I won't have to rot my remaining life away. And guess what? I've found it!"

He let out a weak laughter as he held out his hand. A small capsule containing red liquid was lying in the center of his palm.

"The spell was incomplete. I needed a vast amount of energy."

"And that is why you decided to make use of Gehenna, using Rin to defeat Satan while you take on the rest and harvesting the energy that Satan released after his defeat…" Shura completed his statement as realization dawned upon her.

"That's pretty much it. It was exhausting. I had to plan everything to its details; make sure that nothing goes wrong. If anything goes wrong, I wouldn't be able to fulfill that promise anymore. I guess I owe you an apology for keeping you in the dark. I didn't really want to involve you in any of my crazy plans. And in any case if I die, I wouldn't have to see your heartbroken-face."

"Mephisto…"

"Now take it, Shura. With this, I'll be able to stay by your side forever and you, mine."

"Y-you… you idiot! You big idiot! You could have died out there! Rin could have died! In fact, I could have died!" Shura tightened her fists as her nails dug into the flesh of her palms. Her mouth was slightly opened, showing her tightly gritted teeth.

"It was worth a shot."

Snap.

Shura bent down to Mephisto's level before delivering a hard slap to the surprised demon. The slap echoed through the decrepit surrounding with a satisfying 'thwack'. A red handprint was left behind on Mephisto's cheek. His hand that contained the capsule was quickly withdrawn to prevent it from flying off his palm. Before he could recover from the slap, he was tackled by Shura with a hug. He didn't need to see. He knew she was crying when the smell of fresh tears invaded his nose. A demon has acute sense of smell after all. Despite his throbbing cheek, Mephisto returned the hug, the corner of his mouth curved up slightly as he gave a relieved look.

"Yeah, it was worth it after all."

END

* * *

**Hope you have enjoyed the story! Do review! 3 I may turn this into a long series if I ever get the motivation to write 20k words.**


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